Emergency services were called to Whickham Street in Roker at 3.46pm on Tuesday, February 15, following reports of an explosion at a residential property.
The first fire crews and appliance were on the scene in just five minutes where they discovered that the terraced building had been completely torn apart.
It is reported that the occupant of the ground floor flat had managed to rescue themselves however the occupant of the first floor was still inside the building, prompting firefighters to immediately enter and rescue him.
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Both men were taken to hospital by the North East Ambulance Service (NEAS) where the condition of the man on the first floor deteriorated on Tuesday evening and he remains in a critical but stable condition.
Tyne and Wear Fire and Rescue Service (TWFRS) then used Urban Search and Rescue (USAR) teams and specialist dog units to ensure that no one else was in the building.
He said: "You only have to look at the damage caused to the property to know that it is very fortunate only two people have been injured.
"Everyone at TWFRS wishes them a speedy recovery and I am glad our crews were able to be on scene so quickly to offer them immediate medical assistance with our partners to make the incident safe.
"That emergency response starts with our Fire Control team who received the initial 999 calls and dispatched the crews in the best position to respond. That crew was then on scene in just five minutes.
"Upon our arrival our crews immediately identified that an occupant of the property on question was unaccounted for and they carried out a search of the wreckage.
"An incident of this nature shows the importance of that training and ensures our crews are among the best in the country when responding to an incident of this type.”
Nigel Wilson, Chief Executive Officer at Gentoo, added: “Gentoo was made aware of a major incident at 3:45pm on Tuesday that occurred at two flats on Whickham Street in Roker.
“Reports indicate this may have been a gas explosion, however investigations are continuing. The Health and Safety Executive is carrying out its investigation and we will continue to support them.
“We have been in contact with all of the residents and offered our support. We have found alternative accommodation for some of the residents, while some others have decided to stay with family members.
“We are clearly concerned for the wellbeing of the two confirmed casualties that have been taken to local hospitals. Our thoughts are with the casualties and their families at this difficult time, and we wish them both a full and quick recovery.”